Peter Lynch and Warren Buffett both said that we should invest in what we know. Is it sound advice?
Most of my investing mistakes have been in investing in companies which I didn't understand. You don't need to have your opinion about every company, you just need to know a few ones and invest in them if they are at the right price
Unfortunately, many people invest in the company they know the most, that is, the company in which they are working. Many people have their 401K or other pension investments with a big investments in their own company's stocks. Other people, invest in companies in the sector in which they are working. This is not a good idea.